Abstract: By six-level dry baroclinic model, the influences of upper-level cold vortex on the typyhoon motion are simulated. The diagnostic analyses are carried out by using vorticity equation. It is found that the influence of upper-level cold vortex on typhoon motion is produced through changing the circulation structure around typhoon center. The results also show that the motion is directly related to total vorticity tendency, and this relationship is stable. Meanwhile, it is revealed that total vorticity tendency mainly comes from the horizontal advection of vorticity and divergent term, which means that typhoon motion is controlled by barotropic dynamic factors.